Update the readme with latest run-env.sh and .env information

[GPortas]

Overview of the Feature Request

We should mention in the docs that a new step is now required for setting up the development environment: creating a .env file from .env.example with S3 secrets.

We can also include a more friendly way to setup the environment, by simply running ./run-env.sh unstable without having to worry so much about the images and container registries.

What kind of user is the feature intended for? Frontend devs

What inspired the request? Discussion with @pdurbin

What existing behavior do you want changed? N/A

Any brand-new behavior do you want to add to Dataverse? N/A

Any open or closed issues related to this feature request? N/A